In order to diagnose a traditional X-Ray examination, the images printed on films would be ‘hung’ in front of a light box. For multi-image examinations, as well as for comparison with priors, the ‘hanging’ would often follow a specific protocol. For example, a particular organization or doctor may choose for a two-view chest X-Ray with a two-view prior exam, that the films be hung from left to right as follows: Frontal view of current examination, lateral view of current examination, frontal view of prior examination, lateral view of prior examination. In contrast, the doctor may hang mammography exams with the corresponding views of current and prior next to each other, if that was more appropriate for the diagnostic workflow in that case. Thus, the organization or doctor developed a traditional ‘Hanging Protocol’. Currently, the film and the light box are often being replaced by computer systems, called PACS (Picture Archiving and Communication System). PACS systems can mimic the Hanging Protocols.
Traditional X-Ray examinations typically produce one or a small number of single two dimensional (2D) images. In contrast, the more advanced imaging modalities such as Computer Tomography (CT), Magnetic Resonance Imaging (MRI) or Positron Emission Tomography (PET) can produce dozens of series, each consisting of a hundred or more images. It is possible and not uncommon to review images from these advanced modalities in the same manner as traditional X-Ray images, i.e., by hanging the individual images side-by-side, either on a light-box or using a PACS system.